BirdAnalyst
Species · California · BBS 2025 Release · 1966–2024

Northern Harrier Population Trend in California

All statesGeneralists

Northern Harrier in California has fallen sharply: down 71% on the route-weighted index since 1970.

-71%Since 1970TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
113Routes In StateSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
56YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Northern Harrier Trends in CaliforniaNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

long arc declinecomputed indexTrend sourceWhether the figure is our own computed route-weighted index or an official USGS modeled estimate. The current build labels every trend as computed.Full methodology →

Northern Harrier has fallen sharply in California: down 71% on the route-weighted index since 1970.

Northern Harrier Population Forecast in California

If the recent trend holds, Northern Harrier in California is projected to fall about 12% by 2029 — from 0.21 in 2024 to a central estimate of 0.19 (95% range 0.00–0.46). A 5-year backtest shows a typical error of ±122.8%, with 100% of held-out values landing inside the 95% band.

-12%Change by 2029TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
0.19Projected 2029 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.4695% range95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
±122.8%Backtest errorBacktest errorTypical error when we hold out the most recent years, forecast them, and compare to what actually happened. Lower means a more trustworthy projection.Full methodology →
If the recent trend holds, Northern Harrier in California is projected to fall about 12% by 2029 — from 0.21 in 2024 to a central estimate of 0.19 (95% range 0.00–0.46). A 5-year backtest shows a typical error of ±122.8%, with 100% of held-out values landing inside the 95% band.19682029
Projection of the recent trend (dashed) with 80/95% bands — a projection, not a prediction. Habitat, climate, and land use are not modeled.
YearProjected indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →95% low95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →95% high95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
20250.210.000.48
20260.200.000.48
20270.200.000.47
20280.190.000.47
20290.190.000.46

Northern Harrier Survey Routes in California

Routes recording Northern Harrier in California.
Recent countThe raw number of individuals recorded on this route in its most recent survey year. A single-route tally, not a trend.Full methodology →
Dorris820191972
Atwater720121971
Riovista620241968
Oilfields619991976
Athlone620071973
Collegeville520041968
Yreka520191973
Moreno419861968
Hollister420071974
Davis Creek419981980
Ora Loma420241972
Auburn319801970
Ingalls320001978
Cohasset319991974
Orland320111975
Ventucopa319991975
Brawley320091977
Tranquillity320041972
Hollister 2320212012
Big Pine219931982
Haiwee Res219971996
Palo Verde220212003
Lenwood219951975
Coachella Cn220002000
Lockwood Val219871987

Northern Harrier Population Trend in Other States

alabamaalaskaarizonaarkansascoloradodelawaregeorgiaidahoillinoisindianaiowakansaskentuckylouisianamainemarylandmassachusettsmichiganminnesotamissourimontananebraskanevadanew-hampshirenew-jerseynew-mexiconew-yorknorth-carolinanorth-dakotaohiooklahomaoregonpennsylvaniarhode-islandsouth-dakotatennesseetexasutahvermontvirginiawashingtonwest-virginiawisconsinwyoming

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22.